多項(xiàng)選擇題

Which two statements complete a transaction? （）

A.DELETE employees;
B.DESCRIBE employees;
C.ROLLBACK TO SAVEPOINT C;
D.GRANT SELECT ON employees TO SCOTT;
E.ALTER TABLE employees SET UNUSED COLUMN sal;
F.SELECT MAX(sal) FROM employees WHERE department_id = 20;

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多項(xiàng)選擇題

Which two statements are true about constraints? （）

A.The UNIQUE constraint does not permit a null value for the column.
B.A UNIQUE index gets created for columns with PRIMARY KEY and UNIQUE constraints.
C.The PRIMARY KEY and FOREIGN KEY constraints create a UNIQUE index.
D.The NOT NULL constraint ensures that null values are not permitted for the column.

單項(xiàng)選擇題

What is true about joining tables through an equijoin?（）

A.You can join a maximum of two tables through an equijoin.
B.You can join a maximum of two columns through an equijoin.
C.You specify an equijoin condition in the SELECT or FROM clauses of a SELECT statement.
D.To join two tables through an equijoin, the columns in the join condition must be primary key and foreign key columns.
E.You can join n tables (all having single column primary keys) in a SQL statement by specifying a minimum of n-1 join conditions.